Schools shuttered early and cities warned of probable power outages, as potentially dangerous thunderstorms threatened the Upper Midwest late Monday afternoon.
In northeast Iowa, southeast Minnesota and western Wisconsin, residents were bracing for storms that could bring high winds, tornadoes and hail the size of Ping-Pong balls. The Upper Midwest is accustomed to severe weather, but the high level of risk for very large hail and strong tornadoes caused alarm for state and local officials, who activated emergency operations centers and closed nonemergency city buildings.
“We always have severe weather, I guess, in Iowa,” said Superintendent Joe Carter of the Algona Community School District, about two hours north of Des Moines. “I think the difference with this one is the threat of really, really strong stuff, such as tornadoes, and with a Category 4 ranking of severity.”
A large area that includes Minneapolis and St. Paul is under a relatively high risk (Level 4 out of 5) for severe weather, according to the National Weather Service’s Storm Prediction Center.
At least five school districts across north central Iowa announced early closings on Monday afternoon. The Algona Community School District let out classes at 2 p.m. and canceled afterschool track and golf meets so that buses could get students home throughout the 500-square-mile district before storms descended by early evening.
In the Twin Cities region of Minnesota, Minneapolis closed some city facilities early Monday afternoon and set in motion a team to try to persuade homeless people to take shelter before the storm arrived. In St. Paul, the school district preemptively canceled afterschool activities.
Brennan Dettmann, a local meteorologist at the National Weather Service, said that it was unusual to see such a big storm at this time of year.
“All of the hazards that can come with severe storms are on the table,” he said. “We’re expecting that if the line stays organized, you’re looking at more of a threat from wind and hail. But if it breaks into more scattered storms, the threat of tornadoes goes up.”
He urged residents to have a plan in place to take shelter in case of an emergency.
The Central and Southern Plains are also facing some risk on Monday, particularly across north-central Oklahoma, the Concho Valley and the Rolling Plains of West Texas. In these areas, recent heavy rains have already soaked the ground, increasing the likelihood of flash flooding.
An area spread between the Northern Plains and the Upper Midwest may also be at some risk for heavy rains that could lead to flooding. The Quad Cities and the Twin Cities, along with Milwaukee and Madison, Wis., could see isolated flash flooding.
Chad Hahn, a meteorologist with the National Weather Service in Des Moines, said on Monday afternoon that the agency was tracking thunderstorms developing across northwestern Iowa that had already produced baseball-size hail across the border in Minnesota. Forecasters expected the storms to continue east and grow, both in coverage and intensity, over the next several hours.
“We expect the potential for very large hail, the potential for tornadoes, some that could be strong, and for damaging winds as they move through,” he said. “So definitely an active night that’s unfolding across the state of Iowa.”
In Iowa, Mr. Carter, the school superintendent, said he planned to stay in the office until all buses returned to school property.
“When I go home, like everyone, I’ll be making sure everything outside is secure,” he said. “And then it’s kind of a waiting game. We could very well be looking at a situation where we don’t have any severe weather, and that would be great and best for everyone. But we needed to prepare for the worst scenario.”
Robert Chiarito, Amy Graff and Nazaneen Ghaffar contributed reporting.
